Gradient elution RP-HPLC is used as a suitable method to infer the hydrophobicity values (log K(ow)) of components in complex samples. In this study, the slope (S) and the intercept (log k(w)) of the linear relationship between the logarithm of the retention factor (log k) and the percentage methanol of the eluent (φ) were first obtained by isocratic runs for a set of micropollutants with diverse structures, similar to the contaminants to which the method will be applied. Both S and log k(w) obtained from isocratic runs could be related to log K(ow). Retention times in gradient elution, estimated from these isocratic parameters as a function of log K(ow), were in very good agreement with experimental values and an almost linear relationship can be established between log K(ow) and the retention time. This makes gradient elution RP-HPLC a suitable method to fractionate complex mixtures according to hydrophobicity. Copyright (C) 1999 Elsevier Science B.V.